As disclosed by U.S. Pat. No. 6,007,449 A, there is a well-known conventional transaxle. This transaxle includes a transaxle casing incorporating a hydrostatic transmission (“HST”), a differential gear unit, right and left axles differentially rotatably connected to each other by the differential gear unit, and a reduction gear train for transmitting power from the HST to the differential gear unit. When the interior of the transaxle casing is viewed in plan, the right and left axles are extended rightward and leftward distally from the differential gear unit, the reduction gear train is extended from the differential gear unit perpendicular to the axial direction of the axles, and the HST is disposed in a substantially rectangular HST chamber. If the reduction gear train is assumed to extend forward from the differential gear unit, the reduction gear train defines a left side of the HST chamber, and the right axle defines a rear side of the HST chamber. Therefore, a corner of the HST chamber between the left side and the rear side is adjacent to the differential gear unit.
The differential gear unit constitutes a conventional differential locking mechanism including a thrust collar and a shifter. The thrust collar is fitted on one of the right and left axles so as to be unmovable axially along the axle. The shifter is fitted on the thrust collar slidably along the thrust collar in the axial direction of the axle. Locking pins are extended from the shifter parallel to the axle so as to constantly pierce a differential side gear fixed on the axle. The locking pins are further inserted into respective recesses formed in a bull gear of the differential gear unit so as to lock the right and left axles to each other via the bull gear only when the shifter slides along the thrust collar toward the differential side gear for the purpose of differential locking of the axles. Normally, the shifter is located so as not to insert the locking pins into the recess formed in the bull gear, thereby allowing the right and left axles to rotate differentially.
In the conventional differential locking mechanism, the thrust collar and the shifter are disposed on a distal side of the differential side gear in the axial direction of the axle. In this regard, the above disclosed transaxle is comparatively large-sized, so that the rear side of the HST chamber is spaced forward from the right axle. Therefore, the space between the rear side of the HST chamber and the right axle is used for locating the thrust collar and the shifter, so that the thrust collar with the shifter thereon is provided on the right axle. However, if the transaxle is small-sized, there may be no space between the rear side of the HST chamber and the right axle for locating the thrust collar and the shifter. Further, if the thrust collar with the shifter thereon is provided on the left axle, a portion of the transaxle casing supporting the left axle on the leftward distal side of a differential side gear on the left axle may have to be modified to expand leftward to incorporate the thrust collar and the shifter, thereby conflicting with the demand for minimizing the transaxle, and thereby increasing costs. Therefore, to ensure a small-sized transaxle, it is desired that a differential locking mechanism is minimized, especially, in an axial direction of axles.